Adjust python-stylecheck to skip deleted files and non-py files

Adjust the `CHANGED_FILES` lookup to exclude deleted files as they can't really be checked, and tighten match to files specifically ending with `.py` instead of all files with `py` in them (including this workflow action).

Signed-off-by: Jonas Bardino <bardino@science.ku.dk>

Author: jonasbardino

.github/workflows/python-stylecheck.yml

@@ -21,7 +21,7 @@ jobs:
           fetch-depth: 0  # This is necessary to get the commits
       - name: Get changed python files between base and head
         run: >
-          echo "CHANGED_FILES=$(echo $(git diff --name-only ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }} -- | grep \.py))" >> $GITHUB_ENV
+          echo "CHANGED_FILES=$(echo $(git diff  --diff-filter=ACMRTB --name-only ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }} -- | grep -E '\.py$'))" >> $GITHUB_ENV
       - if: ${{ env.CHANGED_FILES }}
         uses: marian-code/python-lint-annotate@v4
         with: